Catalytic burner arrangement

ABSTRACT

A catalytic burner arrangement including at least a catalytic burner unit with a housing having a reaction chamber in which a catalyst is arranged is provided wherein the catalyst is adapted to react a fuel, particularly a hydrogen containing fluid, with an oxidant, particularly air, for producing heat, the housing having a fluid inlet for supplying a fluid stream into the housing and a fluid outlet for exiting a fluid stream from the housing, and the catalytic burner arrangement further includes a mixing unit forming a mixing chamber in which fuel and oxidant are mixed, wherein the mixing device includes a fuel inlet, an oxidant inlet and an fuel-oxidant-mixture outlet, and wherein the fluid inlet of the catalytic burner unit merges with the fuel-oxidant-outlet of the mixing unit for transferring the fuel-oxidant-mixture from the mixing chamber to the reaction chamber of the catalytic burner unit wherein the fuel inlet of the mixing chamber is arranged upstream of the oxidant inlet of the mixing unit.

BACKGROUND AMD SUMMARY

The present invention relates to a catalytic burner arrangement, as wellas to an auxiliary power assembly.

In auxiliary power units based on a fuel cell technology, energy isprovided by a fuel cell stack. For the operation of the fuel cellusually hydrogen is used. In said APU systems hydrogen is usuallyproduced by so called fuel reformers which generate a hydrogen rich gasfrom hydrocarbon fuels, like diesel, by means of a catalyst. In somepreferred fuel reforming processes, as the autothermal fuel reformingprocess or the steam reforming process, steam is additionally used forthe fuel reforming reaction. The heat required for the production ofsteam may be provided by use of a catalytic burner arranged downstreamof the fuel cell or fuel cell stack, wherein air and excess hydrogenexiting the fuel cell stack are combusted over a catalyst to releaseenergy, which can be used for the steam production.

The known catalytic burners have a housing defining a reaction chamberwith aft inlet for fuel (hydrogen) and an inlet for oxidant (air),whereby fuel and oxidant are introduced into the reaction chamber. Thehousing further incorporates a catalyst, which is arranged downstream ofthe inlets, where hydrogen and air catalytically react with each other.The problem of the known catalytic burners is that air and hydrogenoften react uncontrolled upstream of the catalyst as soon as beingbrought in contact with each other. In some cases air may even enter thefuel inlet, whereby such an uncontrolled combustion may also take placein the pipes. However, these uncontrolled combustions may damage thepipes as well as the burner itself. Additionally, often the mixing ofair and fuel is inhomogeneous, which in turn results in the developmentof hotspots in the catalyst, which might damage the catalyst and produceunwanted emissions.

It is desirable to provide a catalytic burner, which hinders ignition ofthe hydrogen in the pipes and provides a homogenous mixture of air andfuel.

According to aspects of the present invention, a catalytic burner and anauxiliary power unit assembly are provided.

In the following a catalytic burner arrangement is provided whichcomprises at least a catalytic burner unit and a mixing unit. Thereby,the catalytic burner unit comprises a housing which defines a reactionchamber in which a catalyst is arranged. The catalyst is adapted toreact a fuel, particularly a hydrogen containing fluid with an oxidant,particularly air, for producing heat. The housing further has a fluidinlet for supplying a fluid stream into the housing and a fluid outletfor exiting a fluid stream from the housing.

The mixing unit in turn forms a mixing chamber in which fuel and oxidantare mixed and comprises a fuel inlet and an oxidant inlet as well as afuel-oxidant-mixture outlet. The fuel inlet of the catalytic burner unitmerges with the fuel-oxidant-outlet of the mixing unit so that thefuel-oxidant-mixture from the mixing chamber may be transported to thereaction chamber of the catalytic burner unit.

In order to hinder the fuel and the oxidant reacting uncontrolled witheach other and providing an improved mixing, said fuel-oxidant-outlet ofthe mixing chamber is pipe-shaped and extents into the mixing chamber ofthe mixing unit. By means of the pipe-shaped fuel-oxidant-outletextending into the mixing chamber, fuel and oxidant are guided in aswirl around the fuel-oxidant-outlet and are forced to stream upwardsand to change stream direction before the fuel/oxidant mixture may enterthe fuel-oxidant-outlet.

It should be noted that “pipe-shaped” in the context of the presentinvention refers to an elongated hollow element, which may have acylindrical or prismatic form. Said hollow element has at least twoopenings. At least one first opening allows an entrance of thefuel-oxidant mixture into the hollow element and at least one secondopening allows an exit of the fuel-oxidant mixture from the hollowelement and thereby from the mixing unit. Thereby, the at least onefirst opening is arranged inside the mixing chamber. It should befurther explicitly noted that more than one opening as first opening andmore than one opening as second opening may be provided.

According to an alternate solution, said fuel inlet of the mixingchamber is arranged upstream of said oxidant inlet. This staggeredarrangement of the inlets prevents the oxidant from entering the fuelinlet and thereby prevents an uncontrolled ignition of the fuel. Even ifit is preferred to provide in addition a pipe-shaped fuel-oxidant-outletof the mixing chamber which extends into the mixing chamber of themixing unit, the staggered arrangement alone also provides an improvedmixing and prevents uncontrolled combustion.

According to a preferred embodiment, a length of the pipe-shapedfuel-oxidant-outlet extents over the oxidant inlet and/or the fuelinlet. Thereby, it may be preferred if the fuel-oxidant-outlet extendsover both the oxidant inlet and the fuel inlet. In both embodiments, theswirl and the stream redirection may be maximized.

According to a further preferred embodiment, the fuel inlet of themixing chamber is arranged upstream of said oxidant inlet. Thereby, theoxidant is reliably hindered from entering the fuel inlet and reactinguncontrolled.

According to a further preferred embodiment, the fuel inlet and oxidantinlet are arranged angled to a direction of a main fluid streamstreaming through the fuel-oxidant-mixture outlet to the reactionchamber of the catalytic burner. Advantageously, the angled arrangementprovides a homogenous mixture as the fluid needs to be redirected fromthe entrance direction to its exit direction, whereby a mixing of thefluids is performed.

For having a directed fluid stream of a fuel and oxidant, it ispreferred if the fuel inlet and/or the oxidant inlet are designed as atleast one pipe having a longitudinal axis, whereby the directed fluidstreams are provided.

According to a further preferred embodiment, said mixing unit isprismaticly or cylindrical shaped having two basis plates and at leastthree side surfaces or a mantel side, wherein the fuel inlet and theoxidant inlet are arranged in the side surfaces or is the mantel side,and the fuel-oxidant-mixture outlet is arranged at one of the basisplates. Thereby, the geometric design of the mixing unit supports themixing so that a very homogenous mixture may be provided.

According to a further preferred embodiment, at least one of thedirected fluid streams are offset from a longitudinal axis of the mixingchamber, whereby at least one tangential fluid stream is provided. Bymeans of the tangential fluid streams a homogenous mixture may beachieved.

According to a further preferred embodiment, the longitudinal axis ofthe fuel inlet and/or of the oxidant inlet are inclined to a crosssectional plane of the mixing chamber. By the inclined arrangement anuncontrolled ignition of oxidant and fuel and/or an unwanted entering ofoxidant into the fuel pipe is avoided.

According to a further preferred embodiment, the oxidant inlet and thefuel inlet are arranged substantially rectangular to each other, wherebyboth the mixing is improved and an unwanted ignition is reliablyavoided.

A further aspect of the present application relates to an auxiliarypower assembly based on fuel cell technology which comprises at least afuel processing assembly which is adapted to convert hydrocarbon fuelsinto a hydrogen rich gas for fuel cells by using at least hydrocarbonfuel and steam. Downstream of the processor assembly at least one fuelcell or fuel cell stack for providing auxiliary power is arranged.Downstream of the fuel cell a catalytic burner unit is provided which isadapted to burn unused hydrogen exiting from the fuel cell or the fuelcell stack by using an oxidant, such as air or oxygen, and a catalystfor reacting said oxidant and hydrogen to heat, wherein said heat inturn is used for the production of steam used in the fuel processingassembly. Thereby the catalytic burner is designed as described above.

Further embodiments and preferred arrangements are defined in thedescription, the figures and the attached claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be described by means embodimentsshown in the figures. Thereby, the embodiments are exemplarily only andare not intended to limit the scope of the protection. The scope ofprotection is solely defined by the attached claims.

The figures show:

FIG. 1: a schematic illustration of the APU system;

FIG. 2: a schematic view of a first preferred embodiment of thecatalytic burner; FIG. 3: a schematic detailed spatial view of themixing unit shown in FIG. 2;

FIG. 4: a schematic view of a second preferred embodiment of thecatalytic burner; FIG. 5: a schematic detailed spatial view of themixing unit shown in FIG. 4;

FIG. 6: a schematic top view of the mixing unit shown in FIG. 3 and FIG.5 FIG. 7: schematic side views of the mixing unit of FIG. 6.

In the following same or similarly functioning elements are indicatedwith the same reference signs.

DETAILED DESCRIPTION

FIG. 1 shows a schematic illustration of an auxiliary power unit, APU,system 100 based on fuel technology for providing electric power. TheAPU system 100 comprises a fuel reformer 102 which is adapted to producea hydrogen rich gas 104 from a hydrocarbon fuel 105. The hydrogen richgas 104 is introduced into a fuel cell stack 106 arranged downstream ofthe fuel reformer 102. In the fuel ceil stack electric energy 107 isproduced by guiding hydrogen to an anode side of a proton electronmembrane and an oxidant to a cathode side. Excess hydrogen 108, which isnot used in the fuel cell stack may then be transferred to a catalyticburner assembly 110, where the excess hydrogen 108 is reacted with airto produce heat 112. The heat 112 is then used for producing steam 114which in turn is used in the fuel reformer 102 for the conversion ofhydrocarbon fuel 105 to hydrogen rich gas 108. Byproducts from the fuelreforming process and the catalytic burning, such as carbon dioxide andnitrogen oxides, may leave the catalytic burner 110 as exhaust 116.

FIG. 2 and FIG. 4 show schematic illustrations of two alternativeembodiments of the catalytic burner assembly 110. As can be seen fromFIGS. 2 and 4, the burner assembly 110 comprises at least two units,namely a burner unit 10 and a mixing unit 20. The burner unit 10comprises a housing 12 defining a reaction chamber 13 in which acatalyst 14 is incorporated. Further the housing 12 comprises a fluidinlet 16 and a fluid outlet 18. The mixing unit 20 is arranged in closevicinity to the burning unit 10 and adapted to provide a homogenousmixture of air and hydrogen, which is fed through the fluid inlet 16into the housing 12 and to the catalyst 14. The mixing unit 20 itselfcomprises a fuel inlet 22 and an oxidant inlet 24, wherein fuel andoxidant are mixed in a mixing chamber 26 and may exit the mixing unit 20through a fuel-oxidant mixture outlet 28. FIGS. 2 and 4 further depictthat the fuel inlet 22 and the oxidant inlet 24 are angled to a fluidflow direction 30 from the mixing unit 20 to the burner unit 10.

Further, the mixing unit 20 may be cylindrically shaped having a mantelside 32 and two base plates 34 and 36. Instead of the cylindricallyshape also any other prismatic shape is possible, wherein two baseplates 34 and 36 are connected by at least three side surfaces 32.

As can be seen from the first embodiment depicted in FIG. 2, thefuel-oxidant-outlet 28 is a pipe-shaped hollow element and its length Lextends at least over one of the inlets 22; 24 in the mixing chamber 26.By extending the pipe-shaped fuel-oxidant outlet 28 over at least one ofthe inlets 22; 24, the risk of oxidant entering the fuel inlet, whichmay cause uncontrolled combustions, is significantly reduced.Additionally, the fuel inlet may be arranged upstream of the oxidantinlet 24, whereby the risk of uncontrolled combustions is furtherreduced. The pipe-shaped fuel-oxidant outlet 28 further comprises afirst opening 28-1 arranged in the mixing chamber 26 and a secondopening 28-2 which is provided in a bottom plate 34 of the mixing unit20. Thereby it should be noted that more than one opening may beprovided as first and/or second opening 28-1, 28-2.

As illustrated in the second embodiment shown in FIG. 4, the fuel inlet22 is arranged upstream of the oxidant inlet 24, whereby an entering ofthe oxidant into the fuel inlet 22 is avoided. Thereby an unwantedignition of oxidant and fuel inside the fuel inlet 22 is avoided. Incontrast to the illustrated embodiment of FIG. 2, the fuel-oxidantoutlet 28 is not pipe-shaped but designed as simple opening in thebottom plate 34.

In both depicted embodiments, the fuel-oxidant mixture outlet 28 mergeswith the fluid inlet 16 of the burner unit 10. Of course it is alsopossible that the pipe-shaped fuel-oxidant outlet 28 is elongated, orthat a connection pipe is arranged between the burner unit 10 and themixing unit 20, which fluidly connects the fuel-oxidant-mixture outlet28 and the fluid inlet 16.

FIG. 3 and FIG. 5 show detailed spatial views of the mixing unit 20 asshown in FIG. 2 and FIG. 4, respectively. As illustrated in FIG. 3 andFIG. 5, the fuel inlet 22 and the oxidant inlet 24 are arranged at themantel side 32, wherein the fuel oxidant mixture outlet 28 is arrangedat/in the bottom base plate 34. The fuel inlet 22 and the oxidant inlet24 are pipe-shaped providing longitudinal axes A22, A24, whereby adirected fuel stream 38 respectively oxidant stream 40 are provided.These directed streams 38 and 40 are deviated by the walls 32 of themixing unit 20 into a circular motion 41, whereby turbulences areintroduced in the reaction chamber 26. Thereby a mixing of fuel andoxidant is performed. Besides that the mixed gas stream has to undergo astream redirection from the circular motion the linear motion throughthe outlet 28, whereby further perturbations may be caused in the fluidstreams and the homogeneity of the mixing may even be further improved.As can be further seen from FIG. 3, the pipe-shaped fuel-oxidant outlet28 intensifies the induced swirling motion and the redirection of thefluid streams, whereby the mixing is enhanced.

It should be further noted that in case a pipe-shaped fuel-oxidantoutlet 28 is used, the fuel inlet 22 and the oxidant inlet 24 may be onthe same level. Even if an arrangement at the same level is in principlealso possible without a pipe-shaped fuel-oxidant-outlet 28, the risk ofoxidant entering the fuel pipe 22 increases. In this case, it istherefore preferred to arrange the fuel inlet 22 upstream of the oxidantinlet 24 in order to hinder the oxidant from entering the fuel inlet 22.

For providing an optimal mixing the fuel inlet 22 and the oxidant inlet24 are arranged in such a way that the respective fluid streams enterthe mixing chamber tangentially as depicted in the top view of FIG. 6.By the tangential interjection the swirling motion in the chamber 26 andthereby the homogeneity of the mixing may be maximized.

FIGS. 7a and 7b show a further optional detail of the mixing device 20.As can be seen from the illustrated side views, the axes A22, A24 of thefuel inlet pipe 22 respectively the oxidant inlet pipe 24 may beinclined by a predetermined angle α; β in relation to a cross sectionalplane 42 of the mixing unit 20. Usually these angles α; β is relativelysmall, preferably below 10° for ensuring that the fluid streams have asufficiently long stay time in the mixing chamber 26 for developing thedesired homogenous mixture. On the other hand the inclination furtherensures that air streaming through the oxidant 24 does not enter thefuel pipe 22. Thereby the angles α; β may provide the same or adifferent inclination.

In general the inventive mixing unit hinders ignition of hydrogen in thepipes. Additionally, the mixing unit also reduces emissions of unwantedbyproducts produced during the catalytic burning process since allcombustible gases are burned due to the homogenous mixing. Additionally,only little excess air is necessary for reaching complete combustion,and increasing the temperature to the desired temperature suitable formethane combustion performed in the catalyst, which in turn reduces theamount of unwanted byproducts. Consequently, the catalytic burnerefficiency may be maximized as the reactor temperature and hence themethane conversion is quickly in the desired range.

REFERENCE SIGNS

-   100 auxiliary power unit-   102 fuel reformer-   104 hydrogen rich gas-   105 hydrocarbon fuel-   106 fuel cell stack-   107 electricity-   108 hydrogen-   110 catalytic burner-   112 heat-   114 steam production-   10 catalytic burner unit-   12 housing-   14 catalyst-   16 fluid inlet-   18 fluid outlet-   20 mixing unit-   22 fuel inlet-   24 oxidant inlet-   26 mixing chamber-   28 fuel-oxidant mixture outlet 28-1; 28-2 openings-   30 fluid stream direction from the mixing chamber to the reaction    chamber-   32 mantel side-   34 bottom base plate-   36 top base plate-   38 fuel stream direction-   40 oxidant stream direction-   42 cross sectional plane-   L length of fuel-oxidant outlet-   A22 longitudinal axis of fuel inlet-   A24 longitudinal axis of oxidant inlet

1. Catalytic burner arrangement comprising at least a catalytic burnerunit with a housing having a reaction chamber in which a catalyst isarranged, wherein the catalyst is adapted to react a fuel, particularlya hydrogen containing fluid, with an oxidant, particularly air, forproducing heat, the housing having a fluid inlet for supplying a fluidstream into the housing and a fluid outlet for exiting a fluid streamfrom the housing, and the catalytic burner arrangement further comprisesa mixing unit forming a mixing chamber in which fuel and oxidant aremixed, wherein the mixing device comprises a fuel inlet, an oxidantinlet and an fuel-oxidant-mixture outlet, and wherein the fluid inlet ofthe catalytic burner unit merges with the fuel-oxidant-outlet of themixing unit for transferring the fuel-oxidant-mixture from the mixingchamber to the reaction chamber of the catalytic burner unit wherein thefuel inlet of the mixing chamber is arranged upstream of the oxidantinlet of the mixing unit; and wherein the fuel inlet] and the oxidantinlet are arranged angled to a direction of a main fluid streamstreaming through the fuel-oxidant-mixture outlet to the reactionchamber of the catalytic burner.
 2. Catalytic burner arrangementaccording to claim 1, wherein the mixing chamber has two basis plateswhich are connected by at least one side face, wherein the fuel-oxidantis arranged at one of the basis plates and the oxidant inlet is arrangedat the side face, and wherein the fuel-oxidant-outlet of the mixingchamber is pipe-shaped and extents into the mixing chamber of the mixingunit, wherein preferably a length of the pipe-shaped fuel-oxidant-outletextents over at least the oxidant inlet.
 3. Catalytic burner arrangementaccording to claim 1, wherein the fuel inlet and/or the oxidant inlet isdesigned as at least one pipe having a longitudinal axis, whereby adirected fluid stream of fuel and/or oxidant is introduced into themixing chamber.
 4. Catalytic burner arrangement according to claim 1,wherein the mixing chamber is prismaticly or cylindrically shaped,having two basis plates (34; 36) and at least three side surfaces sidesor a mantel side, wherein the fuel inlet and the oxidant inlet arearranged at the side surfaces or the mantel side, and thefuel-oxidant-mixture outlet is arranged at one of the basis plates. 5.Catalytic burner arrangement according to claim 3, wherein the mixingchamber is prismaticly or cylindrically shaped, having two basis platesand at least three side surfaces sides or a mantel side, wherein thefuel inlet and the oxidant inlet are arranged at the side surfaces orthe mantel side, and the fuel-oxidant-mixture outlet is arranged at oneof the basis plates, and wherein the directed fluid streams are offsetfrom a longitudinal axis of the mixing chamber, thereby providing atleast one tangential fluid stream.
 6. Catalytic burner arrangementaccording to claim 3, wherein the longitudinal axis of the fuel inletand/or the oxidant inlet is inclined to a cross sectional plane of themixing chamber.
 7. Catalytic burner arrangement according to claim 1,wherein the oxidant inlet and the fuel inlet are arranged substantiallyrectangular to each other.
 8. Auxiliary power assembly based on fuelcell technology comprising at least a fuel processing assembly which isadapted to convert hydrocarbon fuels into a hydrogen rich gas for fuelcells by using at least hydrocarbon fuel and steam; downstream of thefuel processor assembly at least one fuel cell or fuel cell stack forproviding auxiliary power; and downstream of the fuel cell stack, acatalytic burner unit which is adapted to burn unused hydrogen exitingfrom the fuel cell or fuel cell stack by using an oxidant and a catalystfor reacting oxidant and hydrogen to heat, wherein the heat is used toproduce steam used in the fuel processing assembly, wherein a catalyticburner arrangement according to claim 1 is used.